Interaction of unimolecular micelles of hydrophobically-modified polyelectrolytes with nonionic ionic mixed surfactant micelles

Interactions of random copolymers of sodium 2-(acrylamido)-2-methylpropanes ulfonate and N-dodecylmethacrylamide (DodMAm) with n-dodecyl hexaethylene g lycol monoether (C12E6) With and without added n-hexadecyltrimethylammonium chloride (CTAC) in 0.2 M NaCl aqueous solutions were investigated by fluor escence and light-scattering techniques. The polymers with the DodMAm conte nts (f(Dod)) ranging from 10 to 50 mol % were singly labeled with pyrene (1 mol %) or doubly labeled with pyrene (1 mol %) and naphthalene (4 mol %). These polymers form unimolecular micelles (unimer micelles) owing to intram olecular self-association of polymer-bound dodecyl groups, the compactness of the unimer micelle depending on f(Dod). The unimer micelles of the polym ers with f(Dod) greater than or equal to 30 mol 5 have a particularly compa ct nanostructure where polymer chains are highly collapsed. In the presence of C12E6/CTAC mixed micelles, the polymer with f(Dod) = 10 mol % abruptly undergoes bulk phase separation as the mole fraction of CTAC (Y) in the mix ed micelle is increased to a certain critical level(Y-p) (i.e., Y-p approxi mate to 0.15). With an increase in f(Dod), the bulk phase separation become s significantly less abrupt, accompanying a marked increase in Y-p. For the polymers with f(Dod) greater than or equal to 40 mol %, no such bulk phase separation was observed in a region of 0 less than or equal to Y less than or equal to 0.6. Intrapolymer nonradiative energy transfer indicates that the unimer micelles of the polymers with food greater than or equal to 30 m ol % are unfolded by interactions with C12E6 The formation of soluble polym er-micelle complexes was manifested by an increase in the hydrodynamic radi us (R-h) upon addition of C12E6 to polymer solutions. The Rh for the unimer micelle with f(Dod) = 50 mol % increased from 8.2 to 15.8 nm by the additi on of 5.0 mM of C12E6 at a polymer concentration of 1.5 g/L. The Rh at Y = 0 further increased to 21.5 nm as CTAC was added to Y = 0.07, indicating an interplay of hydrophobic and electrostatic interactions in the complexatio n between the unimer micelle and C12E6/CTAC mixed micelles.